<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        var year=prompt('请输入年份')
        if(year%4==0&&year%100!=0||year%400==0){
            alert('是闰年')
        }else{
            alert('不是闰年')
        }

        var shuzi=1;
        var num=prompt('请输入分数')
        if (num>90){
            shuzi++;
            alert('优秀')
        }else if(num>80){
            shuzi++;
            alert('良好')
        }else {
            alert(shuzi)
        }


        switch (num){
            case 90:
                alert(90);
                break;
            case 80:
                alert(80);
                break;
            default:
                alert('结束了');
        }
    </script>
</head>
<body>

</body>
</html>